In the operation of any vehicle such as a truck or bus, safety mandates the need for a second braking system. Most particularly, there is a need for a braking system which can be used during slippery conditions without causing the vehicle to skid. One specific example where skidding must be avoided is with a trailer truck where jackknifing can occur.
Emergency braking devices in the past have usually involved some type of brake shoe which directly engages the surface of the tire on the wheel. Such a device is useful to stop a runaway vehicle. The control of skidding, however, between the road surface and the vehicle tire is not achieved by such a braking device and one braking operation will destroy the tire on the vehicle which is engaged by the brake shoe. In one device which attempted to avoid skidding, a second set of wheels were placed on the vehicle so that during slippery conditions, there would be twice the contact between the wheels and the road surface. Such a system, however, requires the vehicle to include a second set of retractable wheels, means for retracting such wheels and a means for synchronizing the retractable wheels with the regular wheels.